Method and system for double contrast perfusion imaging

ABSTRACT

The present techniques relate to a techniques for performing cardiac perfusion imaging in order to detect perfusion defects in the myocardium. The present techniques relate to methods for performing cardiac perfusion imaging by performing at least two image acquisitions using different, customizable saturation delay times, which improves the ability to detect defects.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of the filing date of GreatBritain patent application no. GB 2001118.5, filed on Jan. 27, 2020, thecontents of which are incorporated herein by reference in theirentirety.

TECHNICAL FIELD

The disclosure generally relates to a method and system for performingcardiac perfusion imaging in order to detect perfusion defects in themyocardium. In particular, the present disclosure relates to methods forperforming cardiac perfusion imaging by performing at least two imageacquisitions within each heartbeat using different, customizablesaturation delay times, which improves the ability to detect defectswhilst reducing signal ratio between blood and myocardium which reducesdark rim artefacts.

BACKGROUND

Cardiac magnetic resonance (CMR) perfusion imaging is widely used todetect perfusion defects in the myocardium. In a typical examination, acontrast injection is given that perfuses healthy and unhealthy ordefective myocardial tissue in different ways, which in turn generatescontrast in the final image. This contrast enables the defective tissueto be identified by a clinician. To boost contrast, a saturation pulseis employed to saturate the signal. The saturation pulse is separatedfrom a magnetic resonance imaging (MRI) readout module that is used inthe CMR perfusion imaging by a saturation delay time (TS), during whichthe magnetization recovers to baseline. Thus, TS is a key parameter thatgoverns the contrast between healthy myocardium tissue and defective orunhealthy myocardium tissue. Furthermore, the length of TS determines asignal ratio between myocardium and blood (a factor influencingso-called ‘dark rim artifacts’). However, longer than conventionallyachieved TSs (˜100 ms) would enable an increased contrast-to-noise ratio(CNR) between healthy and unhealthy myocardium, which is key for thediagnosis of coronary artery disease, and lower blood/myocardium signalratios with subsequent reduced dark rim artifacts

However, the clinical need to cover multiple slices (e.g. three or four)at base, mid, and apical regions within a single heartbeat constrains TSto be very short. Therefore, TS is suboptimal for the metric describedabove (myocardium to defect CNR, and myocardium to blood signal ratio).Furthermore, it is generally not possible to acquire the same slicelocation at different cardiac phases more than once.

Therefore, there is a desire to provide an improved method and systemfor capturing images to detect cardiac perfusion defects.

SUMMARY

To address these problems, the present techniques provide a method forcardiac perfusion imaging of a heart comprising: applying at least twosaturation pulses during a cardiac cycle; performing at least two imageacquisitions, each image acquisition taking place after one of thesaturation pulses and after a different saturation time delay, and eachimage acquisition comprising simultaneously exciting at least twodifferent slice locations in the heart and simultaneously obtaining atleast two image slices.

The present techniques may be used with any suitable type of magneticresonance imaging (MRI) readout module. For example, the MRI readoutmodule may be any of balanced steady state free precession (bSSFP),gradient echo, echoplanar imaging, etc. It will be understood that theseare non-limiting examples of MRI readout modules.

Conventional two-dimensional acquisition schemes sequentially acquirethree or four slices within the same heartbeat by applying onesaturation pulse for each slice and waiting the same short saturationdelay time before performing the acquisition of another slice. Theconventional two-dimensional acquisition schemes can provide highspatial resolution images, but are unable to acquire the same slice atdifferent cardiac phases more than once. On the other hand,three-dimensional acquisition schemes enable data to be acquired faster,and may be used to perform multi-phase acquisition (i.e. imagingmultiple phases of the cardiac cycle) using the same short saturationdelay time. However, due to the time available to capture each cardiacphase, current three-dimensional acquistion schemes cannot be used toachieve high spatial resolution images in this context.

Thus, the present techniques remove the constraints imposed byconventional slice-by-slice two-dimensional acquisition schemes by usingsimultaneous multi-slice imaging techniques to acquire the same set ofmultiple slices during different cardiac phases within a singleheartbeat, at different delay times. Each multi-slice acquisition in thedifferent cardiac phases is performed after a customisable saturationtime delay. This may advantageously reduce the overall number ofacquisition modules that are needed. The resulting imaging protocolprovides substantially the same spatial coverage as the current clinicalstandard (i.e. that provided by existing 2D slice-by-slice aquisition),but provides at least double temporal coverage and multi-contrast data.

It will be understood that the number of image acquisitions that may beperformed within a cardiac cycle depends on the saturation time delaysused for each image acquisition, the time required to perform eachmulti-slice acquisition, as well as the length of the cardiac cycle(which can vary from person to person, or under different conditionssuch as stress or relaxation). Thus, the present techniques perform atleast two image acquisitions per cardiac cycle.

The step of applying at least two saturation pulses may compriseapplying a first saturation pulse and a second saturation pulse, atdifferent times during the cardiac cycle.

Thus, the step of performing at least two image acquisitions maycomprise: waiting a first saturation time delay after application of thefirst saturation pulse; performing, after the first saturation timedelay, a first image acquisition comprising simultaneously exciting atleast two different slice locations in the heart and simultaneouslyobtaining at least two image slices; waiting a second saturation timedelay after application of the second saturation pulse; and performing,after the second saturation time delay, a second image acquisitioncomprising simultaneously exciting the at least two different slicelocations in a heart and simultaneously obtaining at least two imageslices, wherein the second saturation time delay is of a differentlength to the first saturation time delay. That is, two (or more) setsor blocks of image acquisition may be performed (each obtaining multipleslices) in each cardiac cycle, each after a different time following adifferent saturation pulse. The first saturation time delay may belonger than the second saturation time delay, or vice-versa. The lengthof the first and second saturation time delays may be customized, e.g.selected to suit the patient or the cardiac phase.

The step of performing at least two image acquisitions may compriseusing two-dimensional imaging, simultaneous multi-slice (SMS) imaging,or three-dimensional imaging. SMS imaging, also known as multiband (MB)imaging, employs complex radio-frequency pulses together with parallelimaging coil arrays to acquire several sections along the z-axissimultaneously. This enables a significant reduction in imageacquisition time and the number of acquisition modules which are needed.Since SMS images can be obtained more quickly, it is possible to usedifferent saturation time delays with each acquisition.

The step of performing the first image acquisition may comprisesimultaneously obtaining at least two image slices during a firstcardiac phase, and the step of performing the second image acquisitionmay comprise simultaneously obtaining at least two image slices during asecond cardiac phase. The first cardiac phase may be during end systole,and the second cardiac phase may be during mid-diastole, but these arenon-limiting examples of the cardiac phases during which image slicesmay be obtained. It will be understood that image acquisition may beperformed during any two or more cardiac phases.

Generally, at least two image slices are obtained during each imageacquisition. In a particular example, the steps of performing a firstand second image acquisition may comprise simultaneously obtaining threeimage slices. The three image slices may correspond to basal, mid, andapical segments of the heart, but this is a non-limiting example of thedifferent segments that may be imaged.

As mentioned above, saturation time delays that are longer than thoseused in conventional CMR perfusion imaging techniques may be used in thepresent techniques to improve the signal ratio and contrast-to-noiseratio. Typically, short saturation time delays of around 100 ms may beused in the conventional techniques. Thus, in the present techniques,one of the first saturation time delay and second saturation time delaymay have a length in the range of 50 ms to 150 ms (i.e. a short timedelay), and the other of the first saturation time delay and secondsaturation time delay may have a length in the range of 200 ms to 400ms, or between 200 ms to 600 ms (i.e. a long time delay). It will beunderstood that both the first and second saturation time delays may beshort or long time delays, of differing values. These ranges arenon-limiting examples and the first and second saturation time delaysmay be any suitable values.

The present techniques also provide a (non-transitory) computer readablemedium carrying processor control code that, when implemented in asystem (e.g. executed by an image processor or other suitable processor)causes the system to carry out the methods described herein.

The present techniques also provide an image capture system for cardiacperfusion imaging of a heart. The system may comprise an image capturedevice that is configured to capture images using the method(s)described herein. The system may comprise a user interface which isconfigured to display the images captured by the image capture device.

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

The above mentioned attributes and other features and advantages of thisdisclosure and the manner of attaining them will become more apparentand the disclosure itself will be better understood by reference to thefollowing description of embodiments of the disclosure taken inconjunction with the accompanying drawings, wherein:

FIG. 1 a shows a schematic diagram of an imaging sequence structure fora conventional perfusion imaging protocol;

FIG. 1 b shows a schematic diagram of an example imaging sequencestructure, in accordance with one or more embodiments of the presentdisclosure;

FIGS. 2 a-2 c show the outcome of numerical simulations used to studythe relationship between saturation delay time, contrast between healthyand defective tissue, and signal ratio between blood and myocardium, inaccordance with one or more embodiments of the present disclosure;

FIGS. 3 a-3 b show the outcome of in-vivo evaluation of an exampleimaging sequence structure, in accordance with one or more embodimentsof the present disclosure;

FIGS. 4 a-4 c show a difference in contrast using short saturation timedelays and long saturation time delays, in accordance with one or moreembodiments of the present disclosure;

FIG. 5 shows in-vivo data of an LGE-positive patient, in accordance withone or more embodiments of the present disclosure;

FIG. 6 shows a flow chart showing example steps to obtain images, inaccordance with one or more embodiments of the present disclosure; and

FIG. 7 is a block diagram of a system which may be used to carry out themethod(s) described herein, in accordance with one or more embodimentsof the present disclosure.

DETAILED DESCRIPTION

FIG. 1 a shows a schematic diagram of an imaging sequence structure fora conventional perfusion imaging protocol. In the conventionalacquisition scheme, multiple slices are acquired sequentially or oneafter another within a heartbeat by applying a saturation pulse, waitinga saturation delay time (TS), and obtaining a slice. In the imagingsequence structure shown in FIG. 1 a , three slices are obtained oneafter another of the basal, mid, and apical segments of the heart. Asshown, each slice is obtained at a different time point in a heartbeat,i.e. during a different cardiac phase. Furthermore, each saturationdelay time is the same. As the slices are obtained sequentially, thesaturation delay time has to be short to obtain images of the differentslices within a heartbeat. Accordingly, the resultant images do not havea good signal ratio between myocardium and blood (a factor influencingso-called ‘dark rim artifacts’), or a good contrast-to-noise ratio (CNR)between healthy and unhealthy myocardium, both of which are key for thediagnosis of coronary artery disease, and both of which depend on thelength of TS. Specifically, the signal ratio between myocardium andblood in the resultant images is too high and the CNR is too low.

FIG. 1 b shows a schematic diagram of an example imaging sequencestructure, in accordance with one or more embodiments of the presentdisclosure. The new acquisition scheme comprises applying at least twosaturation pulses during a cardiac cycle, and performing at least twoimage acquisitions, each image acquisition taking place after one of thesaturation pulses and after a different saturation time delay. Eachimage acquisition comprises simultaneously exciting at least twodifferent slice locations in the heart, and simultaneously obtaining atleast two image slices. In FIG. 1 b , two image acquisitions areperformed sequentially (one after the other), but within eachacquisition multiple slices are obtained simultaneously. The saturationtime delay before performing each image acquisition is different andcustomizable.

In FIG. 1 b , each image acquisition is shown as obtaining three slicesof the basal, mid, and apical segments of the heart. It will beunderstood that this is a non-limiting illustrative example. Moregenerally, two or more slices may be obtained during each imageacquisition.

In FIG. 1 b , the imaging sequence structure comprises applying twosaturation pulses, each before an image acquisition block, but it willbe understood that this is a non-limiting illustrative example, and morethan two saturation pulses and more than two image acquisition blocksmay be used in some cases. In this illustrative example, the step ofapplying at least two saturation pulses may comprise applying a firstsaturation pulse and a second saturation pulse at different times duringthe cardiac cycle, wherein the first saturation time delay begins fromthe application of the first saturation pulse, and the second saturationtime delay begins from the application of the second saturation pulse.In other words, in FIG. 1 b , the method comprises applying the firstsaturation pulse, waiting a first saturation time delay, and thenperforming a first image acquisition. Then, the method comprisesapplying a second saturation pulse, waiting a second saturation timedelay, and then performing a second image acquisition. That is, the twosets or blocks of image acquisition shown in FIG. 1 b may be performed(each obtaining multiple slices) in each cardiac cycle, each after adifferent time following a different saturation pulse. In this case, thefirst saturation time delay may be longer than the second saturationtime delay, or vice-versa.

In FIG. 1 b , the first image acquisition is shown as being performedafter a long saturation time delay (LTS), and the second imageacquisition is shown as being performed after a short saturation timedelay (STS). It will be understood that this is a non-limitingillustrative example, and each image acquisition may be performed afterany saturation time delay length.

The step of performing the first image acquisition may comprisesimultaneously obtaining at least two image slices during a firstcardiac phase, and the step of performing the second image acquisitionmay comprise simultaneously obtaining at least two image slices during asecond cardiac phase. The first cardiac phase may be during end systole,and the second cardiac phase may be during mid-diastole, but it will beunderstood that this is a non-limiting example of the cardiac phasesduring which image slices may be obtained.

The steps of performing a first and second image acquisition maycomprise simultaneously obtaining three image slices corresponding tobasal, mid, and apical segments of the heart, but it will be understoodthat this is a non-limiting example of the different segments that maybe imaged.

As mentioned above, saturation time delays that are longer than thoseused in conventional CMR perfusion imaging techniques may be used in thepresent techniques to improve the signal ratio and contrast-to-noiseratio. Typically, short saturation time delays of around 100 ms may beused in the conventional techniques. Thus, one of the first saturationtime delay and second saturation time delay may have a length in therange of 50 ms to 150 ms (i.e. a short time delay), and the other of thefirst saturation time delay and second saturation time delay may have alength in the range of 200 ms to 400 ms, or between 200 ms to 600 ms(i.e. a long time delay). It will be understood that both the first andsecond saturation time delays may be short or long time delays, ofdiffering values. Again, these ranges are non-limiting examples and thefirst and second saturation time delays may be any suitable values.

The step of performing at least two image acquisitions may compriseusing two-dimensional imaging.

Thus, the perfusion sequence of the present techniques provides dualphase and dual contrast data using multi-slice imaging at two differentsaturation delay times, but it is understood that this choice iscustomizable and indeed, for example, trial phase and trial contrastdata should be achievable.

FIGS. 2 a-2 c show the outcome of numerical simulations used to studythe relationship between saturation delay time, contrast between healthyand defective tissue (MD contrast, FIG. 2 a ), and the blood tomyocardium signal ratio (BM ratio, FIGS. 2 b and 2 c ). The impact ofsaturation delay time (TS) on MD contrast and BM ratio were evaluatedusing numerical simulations performed using EPG signal formalism. Thefollowing sequence parameters were employed: flip angle α=45°, TR=2.56ms, start-up pulses=6, number of bSSFP readout pulses=70. For MDcontrast, myocardial T1 (T1 m) and T2 (T2 m) times were set to 250 msand 44 ms respectively. A range of simulated myocardial defect T1/T2times (T1 d/T2 d) were evaluated from 400/46 ms to 1200/50 ms. For theBM signal ratios, both peak blood (T1 m/T2 m=1200 ms/50 ms) and peakmyocardium (T1 m/T2 m=250 ms/44 ms) conditions were simulated. BloodT1/T2 (T1 b/T2 b) simulated range was 28.5/26.5 ms to 168.8/108.7 ms.

FIG. 2 a shows MD contrast plotted as a function of TS and defect T1times (T1 d) simulated at peak myocardium. The dashed line highlightsthe TS/T1 d combination with highest MD contrast. The simulations showedthat MD contrast is maximized for a TS range of 300-500 ms. FIGS. 2 band 2 c show the BM ratio calculated as a function of TS and blood T1/T2times (T1 b/T2 b) at simulated peak blood (FIG. 2 b ) and peakmyocardium (FIG. 2 c ). The simulations show that the BM ratio decreaseswith increasing TS. In both FIGS. 2 a and 2 b , the quantities wereevaluated at k-space center.

FIGS. 3 a and 3 b show the outcome of in-vivo evaluation of an exampleimaging sequence structure, in accordance with the one or moreembodiments of the present disclosure. A proposed prototype sequenceconsists of two image acquisition blocks acquired in each heartbeat withdifferent saturation times, as shown in FIG. 1 b . Specifically, thefirst image acquisition is performed after a saturation time delay of300 ms (“LTS,” FIG. 3 b ), and the second image acquisition is performeda saturation time delay of 130 ms (“STS,” FIG. 3 a ). Three slices(base, mid, apex) are imaged using SMS-bSSFP with GC-LOLA correction anda multiband factor of 3. T-GRAPPA acceleration (R=7) and phaseoversampling (300%) are employed for an effective in-plane accelerationof 2.3. Images were reconstructed with an inline prototype non-lineariterative reconstruction algorithm with spatial/temporal L1regularization. Slice separation is achieved along the phase encodingdirection where the (shifted) slices are reconstructed on theoversampled field of view.

Three triple-band pulses with CAIPIRINHA radio-frequency phaseincrements of −120°, 0°, and 120° for slices 1, 2, and 3 were generatedas the complex summation of a native single band (SB) pulse. Thisachieves shifts in image space of −FOV/3, 0, and FOV/3 for slices 1, 2,and 3, which results in lower g-factor amplification at reconstruction.However, because each band is subject to an independent phase cyclingscheme, the frequency response of the bSSFP signal is also shifted. Forslices 1, 2, and 3, these shifts equal to −⅓, 0, and ⅓ of the nativebSSFP passband interval. The GC-LOLA framework addresses thisundesirable effect by (i) applying an additional slice unbalancinggradient within each TR interval to align the frequency response of eachband, and (ii) adding an additional GC-LOLA phase cycling term to centerthe frequency response of the (now aligned) bands onto the water peak.

The proposed prototype sequence was evaluated in five patients referredfor contrast CMR at 1.5 T using an 18-element body coil and a 32-channelspine coil. All data was acquired using the following parameters:FOV=360×360 mm2, slice thickness=10 mm, resolution=2.3×2.3 mm2, TR=2.56ms, TE=1.09 ms, flip angle α=45°, readout bandwidth=1008 Hz/Px, start-uppulses=6, number of bSSFP readout pulses=70, readout duration=179 ms,total acquisition time within a heartbeat=608 ms. The slice gap wasadjusted for each patient to cover base, mid and apical regions. Eachpatient underwent late gadolinium enhancement (LGE) imaging (one patientwas LGE positive). A contrast dose of 0.075 mmol/kg (4 cases) or 0.150mmol/kg (1 case) was injected. Patients performed an exhale breath-holdduring first pass perfusion.

LTS and STS data were compared as follows: blood pool and leftventricular myocardium were segmented at baseline, peak blood, and peakmyocardial enhancement. Contrast between peak and baseline myocardium(used as a surrogate for defect) is reported. BM ratios at peak bloodand peak myocardium were calculated.

FIGS. 3 a and 3 b show acquired data using saturation delay times (TS)of 130 ms (FIG. 3 a ) and 300 ms (FIG. 3 b ) on one exemplary subjectwithout perfusion deficit. Top to bottom: the three simultaneouslyexcited slices (base, mid, apex). Left to right: baseline frame, peakblood, and peak myocardium.

The results shown in FIGS. 3 a and 3 b are in-line with the simulationresults shown in FIGS. 2 a-2 c . Specifically, across all five patients(where a single patient's data is shown in FIGS. 3 a-3 b ), LTS imagesled to higher peak to baseline myocardium contrast (158±21%, p<0.01), aswell as decreased BM ratio at peak blood (62±13%) and peak myocardium(79±12%). In the LGE-positive patient (FIG. 5 ), myocardial/scarcontrast increased by 158% at peak myocardial enhancement.

FIGS. 4 a-4 c show a difference in contrast using short saturation timedelays and long saturation time delays for the in-vivo testing. Darkversus light bars refer to the images acquired at STS and LTS,respectively. FIG. 4 a shows the measured peak myocardium to baselinecontrast for the five patients. FIGS. 4 b and 4 c shown BM ratiocalculated at peak blood and peak myocardial enhancement, respectively.

FIG. 5 shows in-vivo data of an LGE-positive patient. Specifically, theimages on the left show LGE images taken at base, mid, and apex, and theimages on the right show dual contrast perfusion data acquired at short(bottom) and long (top) saturation delay times TS.

It is clear from the simulations and in-vivo testing that the proposedperfusion sequence of dual phase imaging with two different saturationdelay times enables a 150% increase of myocardial to defect contrast,and a decrease in the blood to myocardium signal ratio by between 60-80%when using a long saturation delay time (LTS), compared to conventionalshort saturation delay time (STS) images.

FIG. 6 shows a flow chart showing example steps to obtain images, inaccordance with one or more embodiments of the present disclosure. Themethod comprises applying at least two saturation pulses during acardiac cycle or heartbeat. The saturation pulses are applied atdifferent times during the cardiac cycle, i.e. during different cardiacphases. The method then comprises performing at least two imageacquisitions, which each take place after a different saturation timedelay following the at least two saturation pulses. Each imageacquisition comprises simultaneously exciting at least two differentslice locations in the heart and simultaneously obtaining at least twoimage slices.

Thus, the method may comprise applying a first saturation pulse (stepS100), waiting a first saturation time delay (step S102), and thenperforming, after the first saturation time delay, a first imageacquisition comprising simultaneously exciting at least two differentslice locations in the heart and simultaneously obtaining at least twoimage slices (step S104). Subsequently, the method may comprise applyinga second saturation pulse (step S106), waiting a second saturation timedelay (step S108), and then performing, after the second saturation timedelay, a second image acquisition comprising simultaneously exciting theat least two different slice locations in a heart and simultaneouslyobtaining at least two image slices (step S110), wherein the secondsaturation time delay is of a different length to the first saturationtime delay.

The operations described and depicted in the illustrative methods ofFIG. 6 may be carried out or performed in any suitable order as desiredin various example embodiments of the disclosure. Additionally, incertain example embodiments, at least a portion of the operations may becarried out in parallel. Furthermore, in certain example embodiments,less, more, or different operations than those depicted in FIG. 6 may beperformed.

FIG. 7 is a block diagram of a system which may be used to carry out themethod(s) described herein, in accordance with one or more embodimentsof the present disclosure. The image capture system comprises an imageprocessor 300 that may be used to perform image processing. An imagingsystem 200, e.g. an X-ray machine, an MRI scanner or the like, capturesimages that are sent to the image processor 300. The outputs from theimage processor 300 may be output to a user 400 via any suitable userinterface 402, e.g. a screen on a computer or other electronic device.

The image processor 300 may be formed from one or more local, remote, orcloud servers.

The image processor 300 may include one or more processors 302, one ormore memory devices 304 (generically referred to herein as memory 304),one or more input/output (“I/O”) interface(s) 306, one or more dataports 308, and data storage 312. The image processor 300 may furtherinclude one or more buses 310 that functionally couple variouscomponents of the image processor 300.

The data storage 312 may store one or more operating systems (O/S) 314;and one or more program modules, applications, engines,computer-executable code, scripts, or the like. Any of the componentsdepicted as being stored in data storage 312 may include any combinationof software, firmware, and/or hardware. The software and/or firmware mayinclude computer-executable code, instructions, or the like that may beloaded into the memory 304 for execution by one or more of theprocessor(s) 302 to perform any of the operations described earlier inconnection with correspondingly named engines and/or methods describedherein in accordance with the various embodiments.

The bus(es) 310 may include at least one of a system bus, a memory bus,an address bus, or a message bus, and may permit exchange of information(e.g., data (including computer-executable code), signaling, etc.)between various components of the image processor 300. The bus(es) 310may include, without limitation, a memory bus or a memory controller, aperipheral bus, an accelerated graphics port, and so forth. The bus(es)310 may be associated with any suitable bus architecture including,without limitation, an Industry Standard Architecture (ISA), a MicroChannel Architecture (MCA), an Enhanced ISA (EISA), a Video ElectronicsStandards Association (VESA) architecture, an Accelerated Graphics Port(AGP) architecture, a Peripheral Component Interconnects (PCI)architecture, a PCI-Express architecture, a Personal Computer MemoryCard International Association (PCMCIA) architecture, a Universal SerialBus (USB) architecture, and so forth.

The memory 304 of the image processor 300 may include volatile memory(memory that maintains its state when supplied with power) such asrandom access memory (RAM) and/or non-volatile memory (memory thatmaintains its state even when not supplied with power) such as read-onlymemory (ROM), flash memory, ferroelectric RAM (FRAM), and so forth.Persistent data storage, as that term is used herein, may includenon-volatile memory. In certain example embodiments, volatile memory mayenable faster read/write access than non-volatile memory. However, incertain other example embodiments, certain types of non-volatile memory(e.g., FRAM) may enable faster read/write access than certain types ofvolatile memory.

In various implementations, the memory 304 may include multipledifferent types of memory such as various types of static random accessmemory (SRAM), various types of dynamic random access memory (DRAM),various types of unalterable ROM, and/or writeable variants of ROM suchas electrically erasable programmable read-only memory (EEPROM), flashmemory, and so forth. The memory 304 may include main memory as well asvarious forms of cache memory such as instruction cache(s), datacache(s), translation lookaside buffer(s) (TLBs), and so forth. Further,cache memory such as a data cache may be a multi-level cache organizedas a hierarchy of one or more cache levels (L1, L2, etc.).

The data storage 312 may include removable storage and/or non-removablestorage including, but not limited to, magnetic storage, optical diskstorage, and/or tape storage. The data storage 312 may providenon-volatile storage of computer-executable instructions and other data.The memory 304 and the data storage 312, removable and/or non-removable,are examples of computer-readable storage media (CRSM).

The data storage 312 may store computer-executable code, instructions,or the like that may be loadable into the memory 304 and executable bythe processor(s) 302 to cause the processor(s) 302 to perform orinitiate various operations. The data storage 312 may additionally storedata that may be copied to memory 304 for use by the processor(s) 302during the execution of the computer-executable instructions. Moreover,output data generated as a result of execution of thecomputer-executable instructions by the processor(s) 302 may be storedinitially in memory 304, and may ultimately be copied to data storage312 for non-volatile storage.

The data storage 312 may further store various types of data utilized bycomponents of the image processor 300. Any data stored in the datastorage 312 may be loaded into the memory 304 for use by theprocessor(s) 302 in executing computer-executable code. In addition, anydata depicted as being stored in the data storage 312 may potentially bestored in one or more of the data stores and may be accessed and loadedin the memory 304 for use by the processor(s) 302 in executingcomputer-executable code.

The processor(s) 302 may be configured to access the memory 304 andexecute computer-executable instructions loaded therein. For example,the processor(s) 302 may be configured to execute computer-executableinstructions of the various program modules, applications, engines, orthe like of the system to cause or facilitate various operations to beperformed in accordance with one or more embodiments of the disclosure.The processor(s) 302 may include any suitable processing unit capable ofaccepting data as input, processing the input data in accordance withstored computer-executable instructions, and generating output data. Theprocessor(s) 302 may include any type of suitable processing unitincluding, but not limited to, a central processing unit, amicroprocessor, a Reduced Instruction Set Computer (RISC)microprocessor, a Complex Instruction Set Computer (CISC)microprocessor, a microcontroller, an Application Specific IntegratedCircuit (ASIC), a Field-Programmable Gate Array (FPGA), aSystem-on-a-Chip (SoC), a digital signal processor (DSP), and so forth.Further, the processor(s) 302 may have any suitable microarchitecturedesign that includes any number of constituent components such as, forexample, registers, multiplexers, arithmetic logic units, cachecontrollers for controlling read/write operations to cache memory,branch predictors, or the like. The microarchitecture design of theprocessor(s) 302 may be capable of supporting any of a variety ofinstruction sets.

Referring now to other illustrative components depicted as being storedin the data storage 312, the O/S 314 may be loaded from the data storage312 into the memory 304 and may provide an interface between otherapplication software executing on the image processor 300 and hardwareresources of the image processor 300. More specifically, the O/S 314 mayinclude a set of computer-executable instructions for managing hardwareresources of the system and for providing common services to otherapplication programs (e.g., managing memory allocation among variousapplication programs). In certain example embodiments, the O/S 314 maycontrol execution of one or more of the program modules depicted asbeing stored in the data storage 312. The O/S 314 may include anyoperating system now known or which may be developed in the futureincluding, but not limited to, any server operating system, anymainframe operating system, or any other proprietary or non-proprietaryoperating system.

Referring now to other illustrative components of the image processor300, the input/output (I/O) interface(s) 306 may facilitate the receiptof input information by the image processor 300 from one or more I/Odevices as well as the output of information from the image processor300 to the one or more I/O devices. The I/O devices may include any of avariety of components such as a display or display screen having a touchsurface or touchscreen; an audio output device for producing sound, suchas a speaker; an audio capture device, such as a microphone; an imageand/or video capture device, such as a camera; a haptic unit; and soforth. Any of these components may be integrated into the imageprocessor 300 or may be separate. The I/O devices may further include,for example, any number of peripheral devices such as data storagedevices, printing devices, and so forth.

The I/O interface(s) 306 may also include an interface for an externalperipheral device connection such as universal serial bus (USB),FireWire, Thunderbolt, Ethernet port or other connection protocol thatmay connect to one or more networks. The I/O interface(s) 306 may alsoinclude a connection to one or more antennas to connect to one or morenetworks via a wireless local area network (WLAN) (such as Wi-Fi) radio,Bluetooth, and/or a wireless network radio, such as a radio capable ofcommunication with a wireless communication network such as a Long TermEvolution (LTE) network, WiMAX network, 3G network, etc.

The image processor 300 may further include one or more data ports 310via which the image processor 300 may communicate with any of theprocessing modules. The data ports(s) 310 may enable communication withthe image capture device 200 and the database 500.

It should be appreciated that the engines and the program modulesdepicted in the Figures are merely illustrative and not exhaustive, andthat processing described as being supported by any particular engine ormodule may alternatively be distributed across multiple engines,modules, or the like, or performed by a different engine, module, or thelike. In addition, various program module(s), script(s), plug-in(s),Application Programming Interface(s) (API(s)), or any other suitablecomputer-executable code hosted locally on the system and/or hosted onother computing device(s) accessible via one or more of the network(s),may be provided to support the provided functionality, and/or additionalor alternate functionality. Further, functionality may be modularizeddifferently such that processing described as being supportedcollectively by the collection of engines or the collection of programmodules may be performed by a fewer or greater number of engines orprogram modules, or functionality described as being supported by anyparticular engine or module may be supported, at least in part, byanother engine or program module. In addition, engines or programmodules that support the functionality described herein may form part ofone or more applications executable across any number of devices of thesystem in accordance with any suitable computing model such as, forexample, a client-server model, a peer-to-peer model, and so forth. Inaddition, any of the functionality described as being supported by anyof the engines or program modules may be implemented, at leastpartially, in hardware and/or firmware across any number of devices.

It should further be appreciated that the system may include alternateand/or additional hardware, software, or firmware components beyondthose described or depicted without departing from the scope of thedisclosure. More particularly, it should be appreciated that software,firmware, or hardware components depicted as forming part of the systemare merely illustrative and that some components may not be present oradditional components may be provided in various embodiments. Whilevarious illustrative engines have been depicted and described assoftware engines or program modules, it should be appreciated thatfunctionality described as being supported by the engines or modules maybe enabled by any combination of hardware, software, and/or firmware. Itshould further be appreciated that each of the above-mentioned enginesor modules may, in various embodiments, represent a logical partitioningof supported functionality. This logical partitioning is depicted forease of explanation of the functionality and may not be representativeof the structure of software, hardware, and/or firmware for implementingthe functionality. Accordingly, it should be appreciated thatfunctionality described as being provided by a particular engine ormodule may, in various embodiments, be provided at least in part by oneor more other engines or modules. Further, one or more depicted enginesor modules may not be present in certain embodiments, while in otherembodiments, additional engines or modules not depicted may be presentand may support at least a portion of the described functionality and/oradditional functionality. Moreover, while certain engines modules may bedepicted or described as sub-engines or sub-modules of another engine ormodule, in certain embodiments, such engines or modules may be providedas independent engines or modules or as sub-engines or sub-modules ofother engines or modules.

Although specific embodiments of the disclosure have been described, oneof ordinary skill in the art will recognize that numerous othermodifications and alternative embodiments are within the scope of thedisclosure. For example, any of the functionality and/or processingcapabilities described with respect to a particular system, systemcomponent, device, or device component may be performed by any othersystem, device, or component. Further, while various illustrativeimplementations and architectures have been described in accordance withembodiments of the disclosure, one of ordinary skill in the art willappreciate that numerous other modifications to the illustrativeimplementations and architectures described herein are also within thescope of this disclosure.

Certain aspects of the disclosure are described above with reference toblock and flow diagrams of systems, methods, apparatuses, and/orcomputer program products according to example embodiments. It will beunderstood that one or more blocks of the block diagrams and flowdiagrams, and combinations of blocks in the block diagrams and the flowdiagrams, respectively, may be implemented by execution ofcomputer-executable program instructions. Likewise, some blocks of theblock diagrams and flow diagrams may not necessarily need to beperformed in the order presented, or may not necessarily need to beperformed at all, according to some embodiments. Further, additionalcomponents and/or operations beyond those depicted in blocks of theblock and/or flow diagrams may be present in certain embodiments.

Accordingly, blocks of the block diagrams and flow diagrams supportcombinations of means for performing the specified functions,combinations of elements or steps for performing the specifiedfunctions, and program instruction means for performing the specifiedfunctions. It will also be understood that each block of the blockdiagrams and flow diagrams, and combinations of blocks in the blockdiagrams and flow diagrams, may be implemented by special-purpose,hardware-based computer systems that perform the specified functions,elements or steps, or combinations of special-purpose hardware andcomputer instructions.

Program modules, applications, or the like disclosed herein may includeone or more software components including, for example, softwareobjects, methods, data structures, or the like. Each such softwarecomponent may include computer-executable instructions that, responsiveto execution, cause at least a portion of the functionality describedherein (e.g., one or more operations of the illustrative methodsdescribed herein) to be performed.

A software component may be coded in any of a variety of programminglanguages. An illustrative programming language may be a lower-levelprogramming language such as an assembly language associated with aparticular hardware architecture and/or operating system platform. Asoftware component comprising assembly language instructions may requireconversion into executable machine code by an assembler prior toexecution by the hardware architecture and/or platform.

Another example programming language may be a higher-level programminglanguage that may be portable across multiple architectures. A softwarecomponent comprising higher-level programming language instructions mayrequire conversion to an intermediate representation by an interpreteror a compiler prior to execution.

Other examples of programming languages include, but are not limited to,a macro language, a shell or command language, a job control language, ascript language, a database query or search language, or a reportwriting language. In one or more example embodiments, a softwarecomponent comprising instructions in one of the foregoing examples ofprogramming languages may be executed directly by an operating system orother software component without having to be first transformed intoanother form.

A software component may be stored as a file or other data storageconstruct. Software components of a similar type or functionally relatedmay be stored together such as, for example, in a particular directory,folder, or library. Software components may be static (e.g.,pre-established or fixed) or dynamic (e.g., created or modified at thetime of execution).

Software components may invoke or be invoked by other softwarecomponents through any of a wide variety of mechanisms. Invoked orinvoking software components may comprise other custom-developedapplication software, operating system functionality (e.g., devicedrivers, data storage (e.g., file management) routines, other commonroutines and services, etc.), or third-party software components (e.g.,middleware, encryption, or other security software, database managementsoftware, file transfer or other network communication software,mathematical or statistical software, image processing software, andformat translation software).

Software components associated with a particular solution or system mayreside and be executed on a single platform or may be distributed acrossmultiple platforms. The multiple platforms may be associated with morethan one hardware vendor, underlying chip technology, or operatingsystem. Furthermore, software components associated with a particularsolution or system may be initially written in one or more programminglanguages, but may invoke software components written in anotherprogramming language.

Computer-executable program instructions may be loaded onto aspecial-purpose computer or other particular machine, a processor, orother programmable data processing apparatus to produce a particularmachine, such that execution of the instructions on the computer,processor, or other programmable data processing apparatus causes one ormore functions or operations specified in the flow diagrams to beperformed. These computer program instructions may also be stored in acomputer-readable storage medium (CRSM) that upon execution may direct acomputer or other programmable data processing apparatus to function ina particular manner, such that the instructions stored in thecomputer-readable storage medium produce an article of manufactureincluding instruction means that implement one or more functions oroperations specified in the flow diagrams. The computer programinstructions may also be loaded onto a computer or other programmabledata processing apparatus to cause a series of operational elements orsteps to be performed on the computer or other programmable apparatus toproduce a computer-implemented process.

Additional types of CRSM that may be present in any of the devicesdescribed herein may include, but are not limited to, programmablerandom access memory (PRAM), SRAM, DRAM, RAM, ROM, electrically erasableprogrammable read-only memory (EEPROM), flash memory or other memorytechnology, compact disc read-only memory (CD-ROM), digital versatiledisc (DVD) or other optical storage, magnetic cassettes, magnetic tape,magnetic disk storage or other magnetic storage devices, or any othermedium which can be used to store the information and which can beaccessed. Combinations of any of the above are also included within thescope of CRSM. Alternatively, computer-readable communication media(CRCM) may include computer-readable instructions, program modules, orother data transmitted within a data signal, such as a carrier wave, orother transmission. However, as used herein, CRSM does not include CRCM.

Although embodiments have been described in language specific tostructural features and/or methodological acts, it is to be understoodthat the disclosure is not necessarily limited to the specific featuresor acts described. Rather, the specific features and acts are disclosedas illustrative forms of implementing the embodiments. Conditionallanguage, such as, among others, “can,” “could,” “might,” or “may,”unless specifically stated otherwise, or otherwise understood within thecontext as used, is generally intended to convey that certainembodiments could include, while other embodiments do not include,certain features, elements, and/or steps. Thus, such conditionallanguage is not generally intended to imply that features, elements,and/or steps are in any way required for one or more embodiments or thatone or more embodiments necessarily include logic for deciding, with orwithout user input or prompting, whether these features, elements,and/or steps are included or are to be performed in any particularembodiment.

What is claimed is:
 1. A method, comprising: performing cardiac magneticresonance (CMR) perfusion imaging by: applying two saturation pulsesduring a cardiac cycle; and performing two image acquisitions, each ofthe two image acquisitions occurring after (i) one of the at least twosaturation pulses, and (ii) a different saturation time delay, whereinperforming the two image acquisitions comprises, for each one of the twoimage acquisitions, (i) simultaneously exciting a set of different slicelocations in the heart, and (ii) simultaneously obtaining a set of imageslices corresponding to the set of different slice locations.
 2. Themethod as claimed in claim 1, wherein applying the two saturation pulsescomprises applying a first saturation pulse and a second saturationpulse at different times during the cardiac cycle, and whereinperforming the two image acquisitions comprises: performing, after afirst saturation time delay after application of the first saturationpulse, a first image acquisition comprising simultaneously exciting theset of different slice locations in the heart and simultaneouslyobtaining the set of image slices; performing, after a second saturationtime delay after application of the second saturation pulse, a secondimage acquisition comprising simultaneously exciting the set ofdifferent slice locations in the heart and simultaneously obtaining theset of image slices, wherein the second saturation time delay is of adifferent length than the first saturation time delay.
 3. The method asclaimed in claim 2, wherein the first saturation time delay is shorterthan the second saturation time delay.
 4. The method as claimed in claim2, wherein the first saturation time delay is longer than the secondsaturation time delay.
 5. The method as claimed in claim 2, wherein oneof the first saturation time delay and the second saturation time delayhas a value in a range of 50 ms to 150 ms, and wherein the other of thefirst saturation time delay and second saturation time delay has a valuein a range of 200 ms to 600 ms.
 6. The method as claimed in claim 1,wherein performing the two image acquisitions comprises using at leastone of two-dimensional imaging, simultaneous multi-slice (SMS) imaging,or three-dimensional imaging.
 7. The method as claimed in claim 1,wherein performing the two image acquisitions comprises: performing afirst image acquisition comprising simultaneously obtaining the set ofimage slices during a first cardiac phase; and performing a second imageacquisition comprising simultaneously obtaining the set of image slicesduring a second cardiac phase.
 8. The method as claimed in claim 7,wherein the first cardiac phase is an end-systole cardiac phase, andwherein the second cardiac phase is a mid-diastole cardiac phase.
 9. Themethod as claimed in claim 1, wherein performing the two imageacquisitions comprises: performing a first and second image acquisitionby simultaneously obtaining three image slices during the first andsecond image acquisition, respectively, corresponding to basal, mid, andapical segments of the heart.
 10. The method as claimed in claim 1,wherein performing the two image acquisitions comprises: using at leastone of balanced steady state free precession, gradient echo, andechoplanar imaging as a magnetic resonance imaging (MRI) readout module.11. The method as claimed in claim 1, wherein the act of performing thetwo image acquisitions comprises: for each one of the two imageacquisitions, (i) simultaneously exciting, as the set of different slicelocations, three different slice locations in the heart, and (ii)simultaneously obtaining, as the set of different image slices, threeimage slices corresponding to the three different slice locations in theheart.
 12. A non-transitory computer-readable medium having processorcontrol code stored thereon that, when executed by a system, causes thesystem to: perform cardiac magnetic resonance (CMR) perfusion imaging ofa heart by: applying two saturation pulses during a cardiac cycle; andperforming two image acquisitions, each of the two image acquisitionsoccurring after (i) one of the at least two saturation pulses, and (ii)a different saturation time delay, wherein performing the two imageacquisitions comprise, for each one of the two image acquisitions, (i)simultaneously exciting a set of different slice locations in the heart,and (ii) simultaneously obtaining a set of image slices corresponding tothe set of different slice locations.
 13. An image capture system,comprising: an imager configured to capture images for performingcardiac magnetic resonance (CMR) perfusion imaging by: applying twosaturation pulses during a cardiac cycle; and performing two imageacquisitions, each of the two image acquisitions occurring after (i) oneof the at least two saturation pulses, and (ii) a different saturationtime delay, the two image acquisitions being performed by, for each oneof the two image acquisitions, (i) simultaneously exciting a set ofdifferent slice locations in the heart, and (ii) simultaneouslyobtaining a set of image slices corresponding to the set of differentslice locations; and a display configured to present the set of imageslices captured by the image capture device.